Preheat the oven at 350ºF (180ºC).
Separate the eggs, place the whites in a large bowl. Beat the yolks with the sugar and the whites to stiff peaks.
Melt the butter and chocolate in the microwave, in careful 30-second increments. Mix until homogeneous and let cool a bit before beating in the sugar and butter mix. Delicately incorporate the beaten whites.
Pour in a 9-inch pan then bake in the oven at 350ºF (180ºC) for 20-25 min.
Serve with whipped cream or a berry coulis.